1. Field of the Invention
The disclosures herein generally relate to an image forming apparatus.
2. Description of the Related Art
Japanese Published Patent Application No. H7-199561 discloses an image forming apparatus which performs a parameter correction process for correcting a control parameter so as to obtain a desired image quality based on a result of detecting image density of a toner image formed on a surface of an image carrier. The image forming apparatus obtains the toner image by developing an electrostatic latent image on a surface of a photoreceptor which is the image carrier using developer including toner and carrier. When the toner in the developer in a developing device is used for the developing, toner density in the developer decreases. Therefore, a control unit in the image forming apparatus supplies toner into the developing device by driving a toner supply device, when a result of the toner density detected by a toner density detection sensor that detects the toner density in the developer in the developing device becomes less than a predetermined target value. According to the above operation, the toner density in the developer is restored. However, even if the toner density is maintained at a constant level, when an environment (temperature or humidity) or a charge quantity of toner fluctuates, the image density of the toner image obtained by the developing may be greater than or less than the target value.
The control unit periodically performs a target value correction process as follows. That is, a test toner image for detecting the image density is formed on the surface of the photoreceptor, and the image density of the test toner image is detected by a reflection type photo sensor. Then, based on a difference between a result of detection and target image density, the target value of the toner density in the developer is corrected, thereby the target image density is obtained. According to the above configuration, even if the environment or the charge quantity of toner fluctuates, an image can be formed having the target image density.
However, in the above image forming apparatus, since test toner images are formed periodically, an amount of consumption of toner increases and the cost of operation rises.